New plan to fight invasive weed at Lake Tahoe

Scientists at Lake Tahoe are trying a new experiment to try to eradicate an invading underwater weed that is spreading through the lake and the Truckee River.

The enemy is the Eurasian watermilfoil, a native of Europe and Asia that showed up in the United States in the 1800s and once was used as an aquarium plant.

The new strategy is to lay black fabric layers over the plant to block its access to sunlight and hopefully snuff it out before it clogs water intakes for the region's primary water supply system.

The Truckee Meadows Water Authority approved $20,000 last week to fund most of the project the U.S. Army Corps of Engineers will manage this summer at Martis Creek Reservoir near Truckee, Calif.

Officials say previous attempts to control it there by mowing the weed may actually have caused it to spread more.

"Definitely we don't want it to get worse. We'd like to control it," said Mark Foree, the authority's general manager.

Sue Donaldson, a water quality education specialist at the University of Nevada, Reno Cooperative Extension, said a lot of eyes will be focussed on the project.

"I'm very interested in this," Donaldson told the Reno Gazette-Journal. "We hope to learn more about where we can use this and how well it works."

The weed spreads rapidly from plant fragments carried from an infected area and can alter severely the ecology of a water body. It forms dense mats that in some cases have even trapped and drowned swimmers, Donaldson said.

Milfoil first was noticed in the Tahoe Keys area of South Lake Tahoe in the late 1960s or early 1970s. Scientists with the U.S. Department of Agriculture documented its spread to other parts of Tahoe in 1995 and the plant has since become prevalent throughout the lake.

While it doesn't grow well in fast-moving sections of the river "it will set up housekeeping anywhere we have slower-moving water," Donaldson said. She said the weed is now flourishing along some slow- moving parts of the lower Truckee River stretching to Pyramid Lake north of Reno.

Over the last five years or so, operators of the water authority's water intake plants in Reno have increasingly had to remove watermilfoil and other aquatic plants from equipment, said Paul Miller, the utility's manager of operations and water quality.

While Miller said the plant has so far only had a "light impact" on operations, officials are taking steps to keep that the case.

Donaldson said the risk is real.

"This stuff clogs," she said, adding that it also could spread by diversion canals into the Carson River system.